2.4. Generation of a novel hypoxia gene signature and calculation of hypoxia score

Our novel hypoxia gene signature was built using robust rank aggregation (RRA)algorithm 13 from the microarray data of hypoxia‐treated HUH7, SNU‐182 and HLF cells. Up‐regulated (fold change > 1.5) mRNAs with P < .05 were selected from the RRA output. 21 mRNAs were included after qRT‐PCR validation under acute, chronic and intermittent hypoxia conditions. To estimate the hypoxia exposure, the hypoxia score was calculated using gene set variation analysis (GSVA). 14 We also compared our 21‐gene hypoxia signature with seven other published hypoxia gene signatures including Buffa’s signature, 9 Eustace's signature, 10 Ragnum’s signature, 11 Sorensen's signature, 15 winter’s signature 16 and Malenstein’s signature. 12 Hypoxia scores based on these seven signatures were also calculated by GSVA. The gene lists of 21‐gene signature were shown in Table S1.